The choice of a semiconductor for switching electrical currents on and off depends on the operating voltage and how much current must be controlled. Silicon is an excellent material for use in low-power transistors, but for high currents and voltages, the implementation of silicon-based switching devices becomes complex and thermal management issues arise.
For high-voltage, high-current devices that can be operated at elevated temperatures, silicon carbide (SiC) is recognized by those skilled in the art as the material of choice for transistor fabrication. The most readily synthesized hexagonal polytypes, 4H and 6H, for SiC substrates have a large indirect band gap (˜3.2 eV) and a large breakdown electric field (2 MV cm−1), as well as high electron mobility (900 cm2 V−1 s−1) and thermal conductivity (400 W m−1 K−1). Given these properties, SiC-based power switches may exhibit performance figures of merit ten to one hundred times that of a silicon substrate switch.
Silicon carbide (SiC) static induction transistors (SITs) are well known in the art. Such transistors may, for example, be used in high power radio frequency (RF) applications. Devices of the SiC SIT type exhibit a superior performance characterized by ultra-low power loss. For example, a known 600 V˜1.2 kV class switching device has been shown to have a breakdown voltage (VBR) of 700 V and a specific on-resistance (RonS) of 1.01 mΩ·cm2.
The fabrication of SiC SIT devices has typically utilized an ionic implantation technique. For example, current fabrication processes use high energy for the n+ region dopant. The dopant implant, however, can cause damage to the SiC substrate leading to concerns with device reliability (such as leakage). To address this concern, the prior art teaches the fabrication of a dual mesa SiC SIT device using a lower energy implant, but this process unfortunately requires an increase in process steps and a higher fabrication cost.
There is accordingly a need in the art to address the foregoing and other concerns with the fabricating of SiC SIT devices.